1. Field of the Invention
The present invention relates to high T.sub.c superconductor and more particularly to fine MgO dispersed Bi-2223 high T.sub.c superconductor.
2. Description of the Prior Art
Since the discovery of high-T.sub.c oxide superconductor, many studies have been made to obtain wire with high critical current density. Microstructural control is important to keep the high critical current density under magnetic field for practical application of superconducting materials. Major problems in BSCCO superconductors are impurities in grain boundary and degradation of Jc under magnetic field due to flux creep. It is relatively easier to process BSCCO superconducting systems to high Jc as compared to YBCO due to their low melting temperature and aligning texturing by a proper mechanical or thermal processing. However, this system exhibits a serious flux creep behavior under magnetic field, requiring very effective flux pinning centers. In YBCO system, it was reported that finely dispersed non-superconducting 211 particles provided flux pinning mechanism. It seems that non-superconducting fine particle which does not react with superconducting matrix can provide flux pinning mechanism.
It is well known that significant magnetic field penetration can occur in the interior of BSCCO superconductors above a critical magnetic field (Hc 1). If the magnetic flux lines within the superconductor are not strongly pinned in place, then Lorentz forces can cause the flux lines to migrate, resulting in resistive energy dissipation. The BSCCO superconductors have been found to exhibit significant flux creep in modest magnetic fields at temperatures well below the critical temperature.
Therefore, the application of these materials in high magnetic fields is seriously limited unless the flux creep is reduced by enhanced flux pinning. The operating temperature and magnetic field will have to be reduced to less than 30K, and few tesla for the BSCCO system. Based on the observation of Yamaguchi et al. who increased the pinning of YBCO ceramics by the introduction of the second phase [see J. Mater.Res. 6, 1404 (1991)], several researchers claimed that Ca.sub.2 CuO.sub.3 increases the pinning of the 2212 and 2223 phase of the BSCCO superconductors. However, the grains of powdered metallurgically processed ceramics are too large (1-100 .mu.m) to act as effective pinning centers.